1. Field of the Invention
The present invention relates to a transmission device assembly, more particularly, to a transmission device for a bicycle, which allows to continuously obtain the forward driving force even if the crank shaft is changed in rotational direction forwardly or reversely.
2. Description of the Prior Art
With a conventional bicycle, forward driving force can be obtained if only a crank shaft is rotated in a forward direction. The bicycle generally includes a forward fork 2 for mounting a front wheel 1 a backward fork 4 for mounting a rear wheel-3 ; and, a frame F having a cross bar 5 for connecting the forks 3 and 4 with each other. The frame F has diagonally extended forward and backward bars 6 and 7 of which the lower end portions are integrally connected to a general hub.
Moreover, a chain gear 8 and a pair of pedals are coupled operationally to the crank shaft 9, and a free wheel 10 is coupled to a backward hub. Also, a driving chain 11 is engaged with the peripheral portions of the chain gear 8 and the free wheel 10 so as to obtain a driving force of the bicycle according to the rotation thereof.
With the transmission device for the bicycle constructed as described above, the driving chain 11 is disposed so that, when the crank shaft 9 is rotated, a sprocket of the free wheel 10 is rotated in a direction equal to the rotational direction of the crank shaft 9. As a result, when the crank shaft 9 is rotated in a forward direction, the forward driving force can be produced. Alternatively, if the crank shaft 9 is rotated in a reverse direction, the forward driving force can't be produced since the sprocket of the free wheel 10 is in an idle state. Accordingly, in order to obtain the forward driving force for the bicycle, the latter must be handled in a constant driving direction. Therefore, there are defects that the driving operation is monotonous and an effect of exercise is insufficient.